1. Field of the Invention
This invention relates to power semiconductor devices and, in particular, to the control of charge recombination lifetime and the turn-off of the same and methods of producing the controlling means.
2. Description of the Prior Art
To reduce turn-off time, and hence a loss in time of switching, in power semiconductor rectifiers and power semiconductor thyristors deep level impurities, such, for example, as gold, platinum, silver, copper and the like, are introduced into the rectifiers and thyristors. Prior art manufacturing procedures embody single or double diffusion process techniques to accomplish the desired end results. However, diffusion processing is not discretionary and therefore the deep level impurities are introduced substantially everywhere into the semiconductor material comprising the rectifier or thyristor. Consequently, the power rectifiers and power thyristors have excessive leakage currents which detrimentally effect the voltage ratings and the temperature ratings of the same. Additionally, the introduction of the deep level impurities into the suitably doped semiconductor material has the tendency to cause the precipitation of the deep level impurity metal at the boundaries of some suitably doped regions, such for example, as phosphorus doped regions and to cause depletion in other suitably doped regions, such for example, as boron doped regions. Such precipitates cause excess leakage to occur at the boundaries.
Therefore, it is an object of this invention to provide new and improved semiconductor devices, such, for example, as power rectifiers and power thyristors which overcome the deficiencies of prior art semiconductor devices.
Another object of this invention is to provide a new and improved semiconductor device having deep level impurities in only selected regions of the devices.
Another object of this invention is to provide a new and improved semiconductor device having directionally solidified regions of semiconductor material including deep level impurities therein.
A further object of this invention is to provide a new and improved process for introducing recombination sites in selected regions of a semiconductor device.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.